The blazing lights of the boxing ring flashed that night in 2012 in Ottawa, Canada, for the “Thrilla on the Hilla”. The beat was heavy, the announcer’s voice loud. In the blue corner was Patrick “Brass Knuckles” Brazeau, a hulking, tattooed, beast of a man, a Canadian navy veteran with a black belt in karate, at 37 the youngest senator by a matter of decades and four years younger than his opponent.

Facing him in the red corner was the then MP for Papineau, one of the smallest electoral district Canada. Regarded by pundits as a national lightweight – a lanky, comparatively slight, pampered pretty-boy, widely seen as insubstantial, a long-haired fop, who people felt rode the coat-tails of his famous prime minister father to a seat in Canada’s House of Commons.

To call the match sensational would be to understate the situation. It may have been for charity, but to think of it as just for fun would be to miss the vast and dramatic symbolism of the event. In Ottawa, it was a sensation.

The boxing match that marked the beginning of his meteoric rise to Canada’s highest office is revisited in a new film currently awaiting theatrical release called God Save Justin Trudeau.

The film-makers, Eric Ruel and Guylaine Maroist, were given unparalleled access and behind-the-scenes footage reveals that the participants – and even then prime minister Stephen Harper – were all too aware of the symbolic importance of the match. The Liberal party had been routed. The Conservatives were a political behemoth, having cast the Liberals into the wilderness.

“Leaderless and penniless, the Liberals have been given up for dead,” the film opens. “One man will change the course of history.”

Ruel and Maroist were extremely busy finishing two other films when they heard about the Trudeau-Brazeau match, they told the Guardian. But they immediately recognised it for what it was. “I thought this was an amazing image,” Maroist told the Guardian. “An amazing metaphor for political life.”

The film is subtitled “or how the member of parliament for Papineau became prime minister of Canada”, and the thesis is clear: that this match was Trudeau’s gambit, that he knew what he was doing, despite the scorn from pundits who thought he would be crushed by Brazeau. The subtext is that, viewed from the perspective of his fight, Trudeau’s spectacular victory in October was exquisitely planned this way from the start.

Asked on film why he’s doing the fight, Trudeau gives a telling answer: “Never underestimate the power of symbols in today’s world … the Liberal party is in a weak position in parliament. We’ve never had so few MPs. The Conservatives have all the money and the support. So … wouldn’t it be fun to see Justin Trudeau win? A triumph over the all-powerful Conservatives?”

“I was put on this planet to do this,” Trudeau is shown telling supporters at the gala before the fight. “I fight – and I win.”

“They all said Trudeau will never go anywhere, he’s a lightweight, he will never even be the Liberal leader,” Ruel told the Guardian. “Even two months before the leadership race was over, the broadcasters were still saying the same thing to us.”

“People were belittling him. People were calling him the Paris Hilton of Canadian politics,” Maroist said. But Trudeau told them, she continued, that if he could put in people’s minds that he could beat the Conservatives, that might change the public’s idea of him. “Because you have to understand,” she added, “being the son of [former prime minister Pierre Trudeau], being establishment, being a very good looking young man, was also something not positive for a politician. I think people underestimated him.”

“But we knew, being very close to the two pugilists, that Mr Trudeau was very focused on winning,” Ruel added. Brazeau, by contrast, was overconfident, and seemed uninterested in strategy.

The match itself, which is played in full in the film, is nothing short of stark. Brazeau comes out swinging, but Trudeau absorbs his every punch, ducking and jumping back. He is light on his feet.

But the bigger senator, by contrast, lumbers around, always chasing, never properly managing to connect a punch. By the third round, he is exhausted, sweat pouring off him. Then Trudeau begins to punish him, pouring punch after punch until the referee steps in.

At no point does Justin Trudeau seem in even the slightest bit out of control. The visual effect of the metaphor is, by this point, inescapable – his victory, when it comes, is inevitable.

After the fight, Trudeau’s rise was meteoric. And, though his party was behind in the polls for much of the election campaign, in hindsight once again it seems as if he was never out of control there, either – while Harper lumbered around with last-minute appeals to Rob Ford supporters.

As for Brazeau, after being humiliated by Trudeau his fall was almost as dramatic as his opponent’s rocket-like ascent. He was abandoned by Harper’s government, and arrested in 2013 on charges of sexual assault and domestic abuse. He was suspended from the senate and briefly managed an Ottawa strip club.

The film, which is awaiting theatrical distribution, is available now on Vimeo.